The present invention relates generally to embroidery sewing machines provided with a zigzag sewing head capable of supplying a string-shaped embroidering material, such as a tape or cord, to a needle drop position (i.e., stitching or sewing position) while zigzagging or swinging (or zigzag-swinging) the material leftward and rightward and then sewing the embroidering material onto a fabric or other sewing workpiece at the needle drop position.
Heretofore, there have been known embroidery sewing machines provided with a zigzag sewing head capable of supplying and sewing a string-shaped embroidering material while zigzag-swinging the embroidering material, such as a tape or cord, onto a fabric or other sewing workpiece, as disclosed in Japanese Patent Publication No. 3145469 or Japanese Patent Application Laid-open Publication No. HEI-8-299639. FIGS. 14 and 15A and 15B are views explanatory of a construction and behavior of the conventional zigzag sewing head provided in such embroidery sewing machines. The conventional zigzag sewing head includes: a vertically-driven needle bar (not shown) having a sewing needle attached thereto; a rotary cylinder 100 disposed around and concentrically with the needle bar for rotation about the axis of the needle bar; and a guide lever 101 pivotably mounted relative to the rotary cylinder 100 via a lever pin 102 for guiding a string-shaped embroidering material T to a needle drop (stitching or sewing) position of the sewing needle. In FIGS. 14 and 15A and 15B, reference character P indicates the current needle drop (stitching) position, Pa the last preceding stitching position, Pb the second stitching position backward from the current stitching position P, and T the string-shaped embroidering material.
In the embroidery sewing machines provided with such a zigzag sewing head, a sewing-progressing direction relative to a fabric (i.e., direction indicated by a black arrow in the figure) is calculated on the basis of predetermined sewing data. Then, sewing operation is carried out, in accordance with the calculated sewing-progressing direction, while rotation of the rotary cylinder is being controlled so that the lever pin 102 is always located straight ahead in the sewing-progressing direction. Further, during that time, the embroidering material T is supplied to and sewn onto a fabric while being zigzag-swung leftward and rightward of the sewing-progressing direction the lever pin 102 in a predetermined pattern through reciprocative swinging movement of the guide lever 101 with the lever pin 102 functioning as a fulcrum point.
With the aforementioned conventional zigzag sewing head, the rotational direction and rotational angle of the rotary cylinder is controlled such that the lever pin 102 is always located straight ahead in the sewing-progressing direction during the sewing operation. Zigzag-swinging movement of the embroidering material T is effected only by swinging movement of the guide lever 101. Consequently, amounts of zigzag-swinging of the embroidering material T depend on an arm length of the guide lever 101 (i.e., length from the lever pin 102 to the lower end of the guide lever 101), and thus, there is encountered a limit in increasing the leftward and rightward zigzag-swinging movement of the embroidering material T. Therefore, in a case where the string-shaped embroidering material T comprises a string and ornaments or accessories attached to the string, such as a beaded string (i.e., string passed through a plurality of beads B), and the embroidering material T has a relatively great diameter, the zigzagged embroidering material T and the sewing needle T may undesirably contact each other, so that the beads B (or ornaments or accessories) and/or the sewing needle may be broken. Such an inconvenience may occur not only with a string-shaped embroidering material T having ornaments or accessories, such as a beaded string, but also with a string-shaped embroidering material T having a great thickness or width.
With the conventional zigzag sewing head shown in FIGS. 15A and 15B, an embroidery frame (not shown) holding the fabric is horizontally moved, in synchronism with swinging movement of the guide lever 101, by an amount of movement calculated by adding a predetermined amount of movement, in the swinging direction of the guide lever 101, to an original amount of stitching movement of the embroidery frame, in order to avoid unwanted contact between the string-shaped embroidering material T and the sewing needle. Namely, as shown in FIG. 15A, when the guide lever 101 should swing rightward (downward in the figure) with respect to the sewing-progressing direction, the embroidery frame too is moved rightward by an amount calculated by adding a predetermined amount to an original amount of stitching movement. Further, as shown in FIG. 15B, when the guide lever 101 should swing leftward (upward in the figure) with respect to the sewing-progressing direction, the embroidery frame too is moved leftward by an amount calculated by adding a predetermined amount to an original amount of stitching movement. With such arrangements, the string-shaped embroidering material T, having already been sewn to the fabric with one or more previous stitches is caused to swing leftward and rightward in response to the movement of the embroidery frame, and thus, the embroidering material T moves greatly away from the needle drop position P. Therefore, even where the embroidering material T has a relatively great diameter, it is possible to prevent unwanted contact between the embroidering material T and the sewing needle. Also, Japanese Patent Publication No. 3763863 discloses a sewing machine which automatically generates zigzag-sewing movement data of the embroidery frame.
FIGS. 16A and 16B show an embroidering material T sewn on a fabric by means of the zigzag sewing head that performs zigzag sewing operation based only on the swinging movement of the guide lever 101, and FIGS. 17A and 17B show an embroidering material T sewn on a fabric by means of the zigzag sewing head that performs zigzag sewing operation based on a combination of the swinging movement of the guide lever 101 and movement of the embroidery frame. More specifically, FIGS. 16A and 17A are each a plan view of the fabric having the embroidering material T sewn thereon, and FIGS. 16B and 17B are perspective views corresponding to the plan views. As seen from the figures, with the zigzag sewing operation based only on the swinging movement of the guide lever 101 involving no movement of the embroidery frame, stitched positions PP are hidden under the embroidering material T, when viewed from above, because the embroidering material T is located right over the stitches. With the zigzag sewing operation based on the combination of the swinging movement of the guide lever 101 and movement of the embroidery frame, on the other hand, stitched positions PP are exposed at opposite sides of the embroidering material T, when viewed from above, because the embroidering material T is located between stitches zigzagged with respect to the sewing-progressing direction. Namely, the zigzag sewing operation based on the combination of the swinging movement of the guide lever 101 and movement of the embroidery frame would require a different sewing design of the embroidering material T from that required of the zigzag sewing operation based only on the swinging movement of the guide lever 101 involving no movement of the embroidery frame.
Further, there have hereto been known so-called “combination embroidery sewing machines” which perform combination embroidery using a pair of a zigzag sewing head and another type of machine head capable performing other sewing operation, such as multi-color embroidery.
Generally, in combination embroidery sewing machines comprising pairs of zigzag sewing heads and multi-color embroidering heads, embroidery frames are provided beneath and in corresponding relation to the pairs of zigzag sewing heads and multi-color embroidering heads. In performing a combination of zigzag sewing and multi-color embroidery sewing onto a sewing workpiece (fabric), for example, “needle-to-needle movement” has to be performed between the zigzag sewing head and the multi-color embroidering head; such needle-to-needle movement is effected by horizontal movement of the embroidery frame. Further, in order to avoid a lower end portion of the guide lever 101, located near the needle drop position, from interfering with the embroidery frame during the horizontal movement of the embroidery frame, the guide lever 101 is manually caused to swing so that the lower end portion of the guide lever 101 is evacuated, prior to the horizontal movement of the embroidery frame, upwardly away from a range of the movement of the embroidery frame. However, if a human operator forgets to evacuate the guide lever 101 prior to the horizontal movement of the embroidery frame, the embroidery frame may interfere with and damage the guide lever 101.